During the oil production, the fluid pressure is needed to be measured and the sample of the fluid from the lower strata is also needed to be taken for locating the oil layer accurately and facilitating the production of the oil.
At present, the tools sold in the market for measuring the fluid pressure at lower strata and for sample taking are provided with detectors driven by piston system, the main disadvantage of these tools are that the contacting area between the detector and the strata is so small that the device cannot enter or leave the well smoothly, leading to the device stuck in the well easily; meanwhile, the detectors are not able to get in touch with the wall of the well uniformly along the circumference, and are not able to control the load exerted on the wall.